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Technical Project PDF
I began this term with the intention of developing a series of ash glazes with the hope of getting similarly expressive effects to those in the wood kiln at HDK. The project would also link in with my growing interest in ‘non-spaces’ through using plants from hedgerows and Cardiff’s invisible edgelands. Looking at the ash glazes of Bernard Leach and Katherine Pleydell Bouverie, I admired the quiet, subtle colours and how they work in a calming way on the viewer. Over the summer I collected together a few different ashes – from our log burning fireplace at home as well as from bracken and rushes I had sourced in the countryside in North Wales. I dry sieved these ashes without washing as I had read in the Phil Rogers glaze book that it wasn’t necessary to wash ashes.
Using the simple 60:40 ash to feldspar ratio recommended by Phil Rogers, I experimented with different feldspars, discovering that Potash crazed the most. I also discovered that increasing the proportion of China Clay made the glaze more matte (Test No1.1). Unfortunately the glaze application on the test tiles is patchy since the tiny amounts of ash I had to work with meant the mixtures ended up containing too much water. I left them to evaporate overnight but the small amount of ash meant I couldn’t get a very thick coverage. A second series of line blends (Test No1.2) was made to see what happened when I added increasing amounts of Potash Feldspar to different ashes. Ideally I would have added increasing amounts of ash instead since these results are too similar. The problems I had with obtaining enough ash led me to work with different glazes instead. All my ash tests were fired in reduction although I did test them in Oxidation too but they were colourless.
I liked one of my ash glaze tests very much because of its matte quality, strong iron speckling and mint green colour (Ash glaze A6 on the PDF) so as result decided to experiment with creating glazes that had a similar quality of subtlety and softness. I came across a glaze I had adapted from Jeremy Jernegan’s dry glaze handbook last year. The original glaze had been a matte white reduction glaze with Potash feldspar being the main ingredient. I had adapted the feldspars (as I did with the ash glazes) and discovered that adding Nepheline Syenite instead created a shiner, more viscous glaze (probably because it is higher in alumina than Potash). As I hoped to use these glazes on functional jars and bowls I didn’t want them to be too matte and flaky.
The original glaze is white however with Nepheline Syenite it becomes blue-white with patches of pink flushing depending on the reduction and application. I wanted a series of glazes with a similar satin quality but in different colours so added metal colourants to the base recipe in proportions as shown in the PDF (Test No2.1) and then, deciding these were too dark, created a Triaxial Blend with the Grey-blue, Turquoise and the lighter base glaze. I added 4 brushed on layers to each of the 16 tiles but unfortunately the results are a lot drier than I expected, not really suitable for functional vessels. The darkness of the glazes is probably a result of using Reduction St Thomas which is a darker clay body than the usual white St Thomas, which I chose because of the iron spotting it encourages. The dryness of the glazes in this test could be a result of them being on the lower level of the gas kiln where they perhaps didn’t quite all reach vitrification temperature.
Having never done a glaze technical before I felt a bit lost as to where to begin and how to alter glazes to get the results I wanted. Although the idea of using natural materials seemed attractive as it fitted with my philosophies of material vitality, finding the materials is such a dedication that it didn’t seem to be practical with the large quantities of glaze I needed for my functional vessels. This project has been valuable to explore how colourants can impact glazes though and made me confident using the reduction kiln which I used for the first time this term.